The present invention relates to fluorine-containing resins, particularly fluorine-containing great resins, and to coating compositions each containing such graft resin.
Hitherto, various fluororesin paints have been used by the reason of superior weather resistance of fluorine-containing copolymer contained therein. Of these paints, there is widely used baking paint which is made up of a mixture of polyvinylidene fluoride and acrylic resin. Furthermore, there have been proposed fluororesins which have cross-linking sites and are suitable for solvent-thinned paints. These fluororesins are widely used as weather resistant paint in various fields such as architectural, automotive and chemical industries. For example, Japanese Patent Unexamined Publication JP-A-57-84107 discloses a fluorine-containing copolymer which is curable at room temperature and comprises a fluoroolefin, cyclohexylvinyl ether, an alkylvinyl ether, and an hydroxyalkylvinyl ether. This hydroxyalkylvinyl ether provides a functional group to the copolymer for curing the copolymer. U.S. Pat. No. 4,631,326 corresponding to JP-A-61-57609 discloses a fluorine-containing copolymer comprising chlorotrifluoroethylene, a vinyl or isopropenyl ester of fatty acid and a hydroxyl-containing allyl ether. This allyl ether provides a functional group to the copolymer for curing the copolymer. Polyvinylidene-fluoride-based baking paints are low in gloss, and thus are not suitable for uses that require high gloss. Paints containing the above-mentioned fluororesins, which have cross-linking sites and are suitable for solvent-thinned paints, are high in gloss, but are inferior in bending test result. Furthermore, these fluororesins are relatively high in price, and thus their uses have been limited.
There have been proposed various fluorine-containing graft resins prepared by graft copolymerization of monomers with fluororesins. These monomers are used for the purpose of improving the coating film in hardness, adhesion property to the substrate, and the like. For example, each of JP-A-59-41315 and JP-A-61-247717 discloses a first graft copolymer prepared by graft copolymerization of a fluorine-containing resin with a monomer. This resin has a reactive C--C double bond and alkoxyl group or cyclohexyloxy group, and this monomer is an ethylenic unsaturated monomer which is copolymerizable with the C--C double bond. JP-A-62-295914 discloses a second graft copolymer prepared by graft copolymerization of a fluorine-containing resin with a monomer. This resin has a reactive double bond by means of urethane bond, and this monomer is an ethylenic unsaturated monomer which is copolymerizable with the double bond. There have further been proposed graft copolymers of fluorine-containing acrylic resins. For example, JP-A-61-43667 discloses a solvent-thinned paint containing a graft copolymer and a polyurethane. This graft copolymer is prepared by graft copolymerization of a monomer with a polymer containing a major constitutional unit derived from an alkylacrylate or an alkylmethacrylate. This monomer is an acrylate or a methacrylate, which has a perfluoroalkyl group. JP-A-2-58513 discloses a fluorine-containing graft copolymer prepared by graft polymerization of a trunk polymer having a particular constitutional unit disclosed therein, with a fluorine-containing monomer which is a fluoroalkylacrylate or a fluoroalkylmethacrylate. JP-A-58-206615 discloses an elastic fluorohyrocarbon resin prepared by graft copolymerization of a fluorine-containing, elastomeric copolymer with at least one fluorine-containing monomer. This copolymer has peroxy groups in the molecule. JP-A-6-25595 discloses a coating composition containing a graft copolymer. This graft copolymer is prepared by graft copolymerization of a vinylidene fluoride polymer with (meth)acrylic ester. This vinylidene fluoride polymer has peroxy group in the molecule.
There is need for baking paints which are reasonable in price and are capable of providing a coated film having high gloss, high weather resistance, and good results in bending test for a long time. Furthermore, there is need for fluororesins which are used as vehicle of baking paints and are superior in solvent solubility, weather resistance, cross-linking property, and adhesion property to various substrates.